The present invention relates to a tool for rotary chip removal, comprising a tool body, a tool tip and means for fastening the tool tip to the tool body. The invention also relates to a tool tip per se, and to a method for manufacturing a tool tip.
It is previously known to use interchangeable cutting edges on different types of tools for chip removal. However this technique has practical limitations due to strength reasons when it comes to milling and drilling tools that rotate about longitudinal axes, since the cutting edges are subjected to variable cutting speed.
Through Karlsson et al. U.S. Pat. No. 5,947,660 there is previously known a drill with an injection molded releasable tool tip anchored in a tool body by means of a pull rod. A drawback with the known drill, as for most drills, is that its not optimized for variable cutting speed. In addition, the thread in the known drill tends to crack at high tension.
It is known, through for example, Foster et al. U.S. Pat. No. 6,086,980, to press a core and a surrounding tube of material powder in two steps. The material powder comprises tungsten carbide (WC) together with cobalt (Co), which is compressed between a stamp and a die and is subsequently sintered such that the binder metal melts and ties the carbides to form a tool for chip removing machining. The object of the known technique is to obtain two different properties depending on radial position in a solid body. Drawbacks with this technique are problems with cracks in the radially external portion or porosities in the radially inner portion.
The present invention has as one object to provide an embodiment of milling or drilling tools with interchangeable cutting edges, whereby said embodiment eliminates the problems of prior art tools.
Another object of the present invention is to provide a rigid tool, preferably for drilling or milling, where the radially external parts of the cutting edges, which are subjected to relatively high cutting speed, have better wear resistance than the radially inner parts of the cutting edges.
Another object of the present invention is to provide a tool, preferably for drilling or milling, where the radially inner parts of the cutting edges, which are subjected to relatively low cutting speed, have higher toughness than the radially external parts of the cuffing edges.
Another object of the present invention is to provide a tool, preferably for drilling or milling, where the risk for tool tip breakage is reduced.
Still another object of the present invention is to provide a tool tip with a thread that endures high tension.
Still another object of the present invention is to provide a method for manufacturing a tool tip from injection molded hard metal whereby the degree of freedom for geometrical appearance is substantially unlimited and whereby grinding work is reduced.
Still another object of the present invention is to provide a method for manufacturing a tool tip from injection molded hard metal whereby cracks and porosities are avoided.
The present invention relates to a rotary chip-removing tool which includes a tool tip including a body having a front end forming an integral cutting edge, and a rear end forming a support surface having a first coupling structure. The tool further comprises a rotary tool body defining an axis of rotation, with a second coupling structure disposed at a front end of the tool body in engagement with the first coupling structure for fastening the rear end of the tool tip against the front end of the tool body. A first portion of the tool tip possesses at least part of the cutting edge and is formed of a first material. A second portion of the tool tip possesses the first coupling structure and is formed of a second material. The first material is more brittle than the second material, and the second material is tougher than the first material.
The invention also relates to a tool tip for rotary chip removal. The tool tip comprises an injection molded body which defines a central axis of rotation and includes front and rear ends. The front end forms an integral cutting edge. The rear end includes a coupling structure adapted to couple the tool tip to a tool body. A first portion of the body possesses at least part of the cutting edge and is formed of a first material. A second portion of the body possesses the coupling structure and is formed of a second material. The first material is more brittle than the second material, and the second material is tougher than the first material.
The invention also relates to a method of manufacturing a tool tip comprised of a body defining a longitudinal axis of rotation and having front and rear ends. The front end forms an integral cutting edge, and the rear end includes a coupling structure adapted to couple the tool tip to a tool body. The method comprises the steps of
A) providing a first heated mixture of a hard metal powder, a plastic binder, and a first amount of metallic binder;
B) injecting the first heated mixture into a first mold cavity;
C) allowing the first heated mixture to cool in the first mold cavity to form a core;
D) providing a second heated mixture of a hard metal powder, a plastic binder, and a second amount of metallic binder less than the first amount of metallic binder;
E) injecting the second heated mixture into a second mold cavity extending around the core;
F) allowing the second heated material to cool in the second mold cavity and adhere to the core; and
G) sintering the core and the second material, wherein the core forms the coupling structure, and the second material forms at least part of the cutting edge.